1. Technical Field
The present invention relates to a liquid crystal display (LCD) device and, more particularly, to an LCD device for preventing occurrence of a tearing effect, and a method for driving the LCD device.
2. Related Art
Recently, display devices have been designed so as to be lightweight and thin like personal computers (PCs) and televisions. For example, the cathode ray tube (CRT) has been replaced by a flat panel display device, such as an LCD device.
The LCD device obtains a desired image signal by application of an electric field to a liquid crystal having dielectric constant anisotropy, the liquid crystal being injected between two substrates, and by controlling the intensity of the electric field so as to control the amount of light, from a backlight, transmitted toward the substrates.
The LCD device is one of most popular flat panel display devices, and a thin film transistor liquid crystal display (TFT-LCD) device is well known.
The LCD device has two driving methods which are classified according to the method for displaying the color image: the color filter method; and the field sequential method.
The LCD device of the color filter method displays a desired image by controlling the amount of light provided to a color filter layer with red (R), green (G) and blue (B) color filters formed on one of the two substrates. That is, the LCD device of the color filter method displays a desired image by controlling the amount of light emitted from a single light source and transmitted to the color filter layer so as to synthesize R, G and B colors.
The LCD device which employs the signal light source and the three-color filter layer to display an image requires unit pixels which respectively correspond to respective R, G and B regions, and thus requires three times as many pixels as a black and white LCD device does. Thus, in order to achieve a high-resolution image, precise technology is required in manufacturing the LCD panel. In addition, it is inconvenient to manufacture because such an LCD device needs the color filter layer, and the brightness is low since light transmittance of the color filter itself is low.
Meanwhile, the LCD device of the field sequential method obtains a full-color image by periodically turning on an independent light source corresponding to R, G and B colors, and color signals corresponding to respective pixels are provided so as to be synchronous with the periodic ON condition. That is, the LCD device of the field sequential method does not define pixels as R, G and B unit pixels, but time-divisionally and sequentially displays R, G and B colors outputted from R, G and B back lights so as to display an image using persistence of vision.
The field sequential driving method is classified into an analog driving method and a digital driving method.
The analog driving method sets a plurality of gradation voltages corresponding to a gradation number, selects one gradation voltage corresponding to gradation data from the gradation voltages, and drives a liquid crystal panel by the selected gradation voltage, so that gradation is displayed by the amount of light to be transmitted in correspondence to the applied gradation voltage.
The digital driving method displays gradation by applying a driving voltage to a liquid crystal constant, and controlling the voltage application time. According to the digital driving method, gradation is displayed by maintaining the driving voltage constant so as to control the accumulated amount of light to be transmitted to the liquid crystal.
In this LCD device, when a frame frequency displayed on a screen and a frequency of data inputted do not match each other, a tearing effect phenomenon occurs in that two or more kinds of data (i.e., data of two more frames) are displayed as a single data. Due to the tearing effect, in the case of the LCD device of the color filter method, data of two or more frames are divisionally displayed as a single data, and in the case of the field sequential method, a certain R, G or B color is updated with data of the next frame so that a different color is displayed, resulting in phenomenon such as dot crawl.
In order to resolve the above problems, the LCD device of the color filter method has been employed by changing a frame frequency displayed on a screen at the same speed as a frequency of data inputted. However, the method for changing the frequency can cause a problem in that it adversely affects gradation when it is applied to the LCD device of the field sequential method. It is because the field sequential method requires a frequency which is three times faster than that required by the color filter method since it is driven in such a way that one frame is divided into an R field, a G field and a B field. However, if frequency is changed to resolve the tearing effect, a problem in representation of gradation may occur.